Combustion of fuel, particularly carbonaceous materials such as fossil fuels and waste, results in hot flue gas streams that contain impurities, such as mercury (Hg), sulfur oxides (SOx), nitrogen oxides (NOx), and particulates, such as fly ash, which must be removed or reduced to a more acceptable level prior to release of the flue gas to the environment. In response to regulations in place in many jurisdictions, numerous processes and equipment systems have been developed to remove or reduce impurity levels and/or particulates in flue gas.
Typical methods of reducing flue gas particulates, Hg, NOx, and SOx impurities from steam generating boilers powered by fuel combustion is through the use of flue gas treatment equipment. Such equipment includes electrostatic precipitators (ESP), fabric filter bag houses, selective catalytic reduction (SCR) systems, wet flue gas desulfurization (WFGD) systems and/or dry flue gas desulfurization (DFGD) systems.
In some flue gas stream processing systems, removal of acidic components, such as SOx, is facilitated through the use of a DFGD system, wherein a reagent slurry or solution is dispersed in the flue gas stream to react with the SOx present therein. Current DFGD systems utilize spray dryer absorber vessels equipped with an atomizer system that receives a reagent slurry, typically in combination with a dilution liquid, and disperses it within the vessel for contact with the flue gas. Upon contact, the reagent slurry reacts with the impurities to produce dry powder products and a flue gas stream of reduced impurity content.
U.S. Pat. No. 4,226,603 discloses an atomizing device arranged centrally in an atomizing chamber. A processing gas is supplied around the atomizing device through a conical guide duct communicating with a horizontal spiral duct through an annular mouth. Processing gas distribution is adjusted by deflection of the gas stream from the spiral duct into the conical guide duct by means of two separate sets of stationary guide vanes arranged relatively close to and overlaying each other in the mouth. A damper is arranged along the mouth to control the ratio of the portions of the gas stream conducted into each of the two vane sets.
U.S. Pat. No. 4,481,171 discloses a spray reactor for flue gas desulfurization equipped with an atomizing disc to spray an alkaline reagent into the flue gas. Concentric inner and outer annular passages around the atomizing disc convey the flue gas. The outer passage flow is controlled by a series of dampers adapted to maintain a relatively constant flow velocity in the inner passage in response to turndown of the load.
U.S. Pat. No. 4,519,990 discloses an atomizer located in an upper portion of a chamber for introducing a finely dispersed spray of aqueous medium, and a gas injection means for receiving a major portion of a hot gas stream for introduction circumferentially about the atomizer. An essential feature of the apparatus is that a minor portion of the hot gas stream is introduced into the chamber in a direction counter to the direction of swirl of the major portion of the hot gas stream passing downwardly through the chamber from about the atomizer.
U.S. Pat. No. 4,560,543 discloses an absorption chamber in which a stream of waste gas is injected downwards from an upper part thereof with an aqueous liquid containing an absorbent atomized into the gas stream. The water content of the aqueous liquid is adjusted depending on the drying capacity of the downward gas stream so the drying of the atomized liquid produces a particulate material having a moisture content of at least 3 percent by weight, to at least 10 percent by weight. A second gas stream is introduced upwards from a bottom part of the absorption chamber at a rate sufficient for fluidizing the moist particulate material within the absorption chamber.
U.S. Pat. No. 4,571,311 discloses a process gas treatment chamber with a pair of concentric, inner and outer annular gas inlet ducts surrounding a liquid spray apparatus. Partition means divide a spiral supply duct into independent inner and outer sub-ducts which define separate inner and outer flow passages connected respectively to the inner and outer annular gas inlet ducts. Damper means are provided in the inlet to the outer sub-duct to selectively control the flow of process gas there through as a means of maintaining the velocity of the flow of process gas through the inner flow passage at a minimum acceptable velocity.
U.S. Pat. No. 4,619,404 discloses a gas distribution arrangement with a helical inlet duct through an annular orificial slit for processing gas introduction into a space between two coaxial guide walls. Guide vanes are provided in the orificial slit to impart a change of direction to the flow of processing gas. Each guide vane is a spatial body with differently extending, vertical limitation surfaces which between adjacent vanes delimit ducts whose sectional area as measured transversely of the flow direction of the processing gas through the individual duct is substantially of the same size over the extent of the duct. The vertical height of the guide vanes may decrease along their radial extent inwards in the orificial slit, and their vertical limitation surfaces may form an acute angle at the radially innermost ends of the guide vanes.
Delivery of a reagent slurry or solution to an atomizer system such as one or more of those described above, in combination with a dilution liquid, typically results in scale buildup. Scale buildup causes plant or system shut downs for necessary cleaning and/or maintenance. Plant or system shut downs, as well as the related cleaning and maintenance of the system and/or plant, is time consuming and costly.
Further, in the case of larger capacity SDA vessels of approximately 12 to approximately 22 meters or larger in diameter, which are desirable to reduce capital expenditures and reduce equipment footprint requirements, scale buildup is even a greater issue. Current dispersers do not allow slurry droplets to penetrate the flue gas sufficiently under higher volume flue gas stream flow as characteristic through the larger capacity SDA vessels. The higher volume flue gas stream thereby readily suppresses downwardly the droplet spray cloud within the SDA vessel. Droplet spray cloud suppression in turn causes poor contact between the reagent slurry and flue gas, resulting in low SOx removal efficiency. Attempts to address low SOx removal efficiency by using an increased number of dispersers within the larger capacity SDA vessels of approximately 12 to approximately 22 meters or larger in diameter, results in additional problems. Such additional problems include intense droplet impactions on vessel walls and significant scale buildup thereon with associated high reagent consumption and cost. Accordingly, an efficient and economical disperser for use in larger capacity SDA vessels of approximately 12 to approximately 22 meters or larger in diameter, that avoids disperser shroud deposits, avoids spray cloud suppression, avoids vessel wall deposits and achieves extended droplet penetration through the flue gas for required impurity removal efficiency with reduced absorbent material consumption is needed.